Having the same problem. Game runs smooth for the most part but when it comes to rendering lots of changes fast it craps its pants lol. And I have a pretty decent card...I heard of people with 780s having problems and all.
I'm really disappointed about how they dealt with car pursuits. The traffic lights are usually what you end up using to stop someone and they are done in a really silly way. For example when you trigger them, the enemy driver being chased seems to "forget" how to drive or steer at that point and just rams into random traffic rather than random traffic ramming into him in a spectacular accident. Not to mention that even after these accidents the drivers always survive and still get out the car to shoot at you.
Apart from that I've been having fun with it. There's so much content to explore it's well worth the money. Those digital trip minigames are REALLY good and well thought about. Love the Spidertank one albeit I wish it was longer and had more variety/levels. Hell, that could be a game on its own! Love just getting my phone out and reading about people as I'm walking by. The town feels really alive and so much so that when it starts raining you actually see the AI pedestrians looking at the sky and acknowledging it and you see less people on the street for a while.
There's minor kinks that bug me like sometimes you end up hacking the wrong thing depending on your point of view when you look at things, as I said the driving AI is quite unimpressive and needs more work, the safe houses are a bit pointless apart from the main one which is awesome and I somewhat wish there were more cars as they all feel kinda the same but apart from that, absolutely solid game! Love Chicago, every single corner looks different they must have spent ridiculous amounts of time on building this sandbox! Every building is different and the textures and level of detail is great! Solid example of a next-gen game. Unique, graphically stunning, story seems quite fresh and it fits on 3 DVDs lol.
